A top UN advisor on climate science says world politicians are not acting fast enough to tackle global warming.

Halldor Thorgeirsson is the science co-ordinator for the upcoming UN climate conference in Montreal.

He admitted the political process was not moving at a speed to satisfy scientists who wanted to see large cuts in greenhouse gas emissions.

And he accepted also that business needed more clarity on future targets so it could plan its investments.

"It is quite clear that we have committed ourselves with the carbon dioxide that is already in the atmosphere to further warming, and it is extremely important to take action immediately to reduce the risk of actually seeing major consequences," he told BBC Radio 4's Today programme.

Mr Thorgeirsson said the prognosis was extremely worrying and the best we could do was to minimise damage by cutting emissions of greenhouse gases and learning to adapt.

Developing countries which had not contributed to the climate problem would suffer from it most, he warned.

"It is quite clear this problem has very significant ethical dimensions and one of those dimensions is that [the people] who have least contributed to the problem are first to see the consequences," he said.

Mr Thorgeirsson hoped the Montreal conference would agree new funds for poor countries to adapt to more droughts or rising sea levels, though he admitted that the cash was unlikely to be sufficient.

He welcomed the signs that business was taking the climate issue seriously and recognised its need for clarity on emissions targets beyond the first Kyoto commitment period of 2012.

However, the politicians may be wrangling over the next set of targets until 2010, making technology investment planning near impossible.

"There is a need for decisive action and that's why there is need for political leadership such as that provided by Tony Blair and others," he said.

The 11th meeting of governments brought together the United Nations Framework Convention on Climate Change (UNFCC) takes place in Montreal, Canada, from 28 November to 9 December.